Alarm circuit for monitoring the primary winding of a neutralizing transformer and its grounding connection

ABSTRACT

A remote alarm and indicating circuit for the primary of a neutralizing transformer utilizing an oscillator to produce balanced opposing signals in the primary and grounding circuits. These signals also flow through the coils of a differential relay in such a manner that if the ground circuit opens or if there is an appreciable change in its impedance or resistance, on the order of 5 percent or more, the differential relay will operate denoting such an occurrence.

United States Patent Allen (541 ALARM CIRCUIT FOR MONITORING THE PRIMARYWINDING OF A N T LIZING TRANSFORMER AND ITS GROUNDING CONNECTION [76]Inventor: Gordon Y. R. Allen, 4 Ireland Court, lslington, Ontario,Canada [22] Filed: Jan. 17, 1972 21 Appl. No.:'218,108

[52] US. Cl. 3 17/18 B, 317/27 R, 324/51,

[51] Int. Cl. ..H02h 3/28 [58] Field oiSearch....317/18 D, 27 R, 18 B;324/51;

L0 C AL OSCILLATOR CURRENT PATHS FLUX PATHS ill] 3,723,813

[ Mar. 27, 1973 [56] Reierences Cited UNITED STATES PATENTS 3,641,3932/1972 Florance et al ..317/l8 D 3,676,737 7/1972 Garzon PrimaryExaminer-James D. Trarnmell Att0rney-Edwin E. Greigg [57] ABSTRACT v Aremote alarm and indicating circuit for the primary of aneutralizingtransformer utilizing an oscillator to produce balanced opposing signalsin the primary and grounding circuits. These signals also flow throughthe coils of a differential relay in such a manner that if the groundcircuit opens or if there is an appreciable change in its impedance orresistance, on the order of 5 percent or more, the differential relaywill operate denoting such an occurrence.

6 Claims, 5 Drawing Figures ll l8 Patented March 27, 1973 2 Sheets-Sheet1 EEK VS:

25E C353 m Patented March 27, 1973 3,723,813

2 Sheets-Sheet '2 um um ALARM CIRCUIT FOR MONITORING THE- PRIMARYWINDING OF A NEUTRALIZING TRANSFORMER AND ITS GROUNDING CONNECTOR Aneutralizing transformer for use in a communication circuit is used toprovide neutralization for a rise in electric power ground potentialand/or longitudinally induced voltages caused by communication linesentering electric power stations or otherwise exposed to the influencesof induced voltages due to their proximity to high voltage transmissionlines.

. In the case where the neutralizing transformer is used to neutralizethe effects of power station ground potential rise, one side of thetransformer primary is usually connected to the substation groundingmat, and the other side is connected to a remote ground outside theinfluence of the power station ground by means of a conductor. Thisconductor is often carried back as far as the telephone central officeground by means of the use of combinations of cable sheath, cablemessenger or spaced pairs connected in parallel in the cable.

Under normal operating conditions, it is rare that the power stationground potential rises and so the current through the neutralizingtransformer is nil. Rises in ground potential appear usually under faultconditions in the power network and it is under these conditions thatthe transformer is called upon to operate. The difference in potentialexciting the primary induces a voltage in the secondary winding of thetransformer.

It is important that the neutralizing transformer circuit be maintainedintact since an open circuit anywhere from the substation ground to theremote ground would cause the transformer to be inoperative, therebyallowing extraneous signals to enter the communication system. It istherefore desirable to monitor the operation of the neutralizingtransformer primary grounding circuit to ensure its operation when it isneeded. An alarm circuit to monitor the primary circuit must not bedirectly connected to the primary winding because during operation,substantial voltages are developed and these voltages could be hazardousto personnel. It is also desirable to be able to detect a potential opencircuit before it occurs.

The circuit described in the following specification not only senseswhen the primary winding circuit of the neutralizing circuit is open,but under certain circumstances, detects a potentially open circuit byreacting to smaller changes in impedance rather than a completely opencircuit, thus giving notice that corrective actions must be taken.

Further, an alarm circuit should be of such a design that it will notadd erroneous signals of its own to the communication circuit.Advantageously, the present invention is balanced so that the resultantcurrent due to the alarm circuit within the primary winding circuit ofthe neutralizing transformer is zero. Thus the secondary sees no effectfrom the alarm circuit being used.

It is the principal object of this invention to provide a circuit whichwill monitor the continuity of the primary grounding circuit of aneutralizing transformer and initiate a visible or audible alert signalupon failure of continuity.

Another object of this invention is to provide a monitor circuit tomonitor the continuity of the primary winding ground circuit of aneutralizing transformer which will not have a direct electricalconnection to the a primary of the transformer.

It is a further object of this invention to provide a monitor circuitfor the primary winding ground circuit of a neutralizing transformerwhich will not excite the primary winding orinduce voltages in anymanner.

A still further object of this invention is to provide a monitor circuitfor the primary winding ground circuit of a neutralizing transformerwhich can be adjusted to correct for seasonal changes in ground mat toground resistance or other arbitrary changes in the ground circuit suchas a change in the number of pairs used without affecting the sensing ofa true open circuit.

These and further objects will become clear upon a careful study of thefollowing specification together with the appended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of the circuitshowing the primary winding and grounding circuit and the monitorcircuit coupled to it;

FIG. 2 shows an equivalent circuit of one-half of the alarm circuit;

FIG. 3 shows an equivalent circuit of the second half of the alarmcircuit;

FIG. 4 shows an equivalent circuit as in FIG. 2 but with the primarywinding ground circuit open; and

FIG. 5 shows an equivalent circuit as in FIG. 3 but withtlie primarywinding ground circuit open.

DESCRIPTION OF THE EMBODIMENTS Referring now to FIG. I there is shownsubstation ground mat 1 9 which is in intimate contact with the ground.Attached to one side 12 of the primary winding 13 of neutralizingtransformer 14 is a grounding cable 11. Attached to the other side ofprimary winding 13 at point 15 is a long grounding cable 16 whichextends to remote ground 17. Ground 17 is sufficiently remote fromground mat 10 so that it is outside the influence of ground potentialchanges at grounding mat 10. Secondary winding 18 is shown forillustrative purposes and it is connected in a conventional manner to autilization device (not shown) which is well known to the art.

7 Turning to the uppermost portion of FIG. 1, one observes localoscillator19 connected to output transformer primary winding 20 by wires21 and 22. Output transformer secondary comprises two identical windings23 and 24. Winding 23 is made identical to winding 24 and wound so thatthe voltage developed across winding 23 from one end connection point 25to the other point 26 is equal and has the same'polarity as that ofsecondary winding 24 between end connections 27 and 28. Thus, forexample, the lower ends of each winding will be positive at the samemoment and/or vice versa.

Point 25 of secondary winding 23 is connected by wire 29 to one end ofcoil 30 of differential relay means 3] at point 32. The opposite end 33of coil 30 is connected by wire 34 to the slider 35 of potentiometer 36for purposes to be described later.

In a like manner the upper end point 27 of secondary winding 24 isconnected by wire 37 to one end point 39 of the second coil 38 ofdifferential relay means 31 so that the polarity and therefore the fluxof coil 38 is opposite to that in coil 30 when the voltages in secondarywindings 23 and 24 are the same.

The opposite end of coil 38, point 40, is connected by wire 41 to theopposite end of secondary winding 23 at point 26. From point 26, a wire42 is connected to one side of capacitor 44, the opposite side of whichis connected by wire 45 to one end of primary transformer winding 13 atpoint 15. The other end of secondary transformer winding 24, point 28,is connected by wire 43 to one side of capacitor 46, the opposite sideof which is connected by wire 47 to the opposite end point 12 of primarywinding 13.

Turning to the right hand portion of FIG. 1, one observes that the lowerend point 48 of potentiometer winding 49 is connected by wire 50 to oneside of capacitor 51, the opposite side being connected by wire 52 topoint 53 in close proximity to remote ground mat 17.

One skilled in the art will realize from this construction thatcapacitors 44, 46 and 51 are isolating capacitors which have a very highimpedance at 60 Hz, the frequency of the current found normally in theneutralizing transformer primary, thus they represent an open circuit atthis frequency. The frequency of the local oscillator means 19 must bechosen, however, so that impedance of said capacitors is very low atlocal oscillator frequency, so that said capacitors representessentially a short circuit at the local oscillator frequen- Referringnow to FIG. 2, there is shown the equivalent circuit loop driven bysecondary winding 24 of output transformer 54 in which resistances 55and 58 represent the total ground and cable resistance between groundingmat and remote grounding mat 17. Cable 16 is represented by a resistor58 in series with ground resistance 55, the resistors being connectedbetween the ends of the primary winding points 12 and 15.

As will be obvious to those skilled in the art, the current produced bythe voltage changes in secondary winding 24 flows through capacitor 46and divides at point 12 into two parallel paths between points 12 and15, one path through the primary transformer winding 13 and the secondpath through resistance 55, the cable 16 represented by resistor 58 inthis diagram. The value of the current through each path is inverselyproportional to the respective path impedance at the output frequency oflocal oscillator 19. The arrows represent the direction of current flowwhen the lower end of secondary winding 24 swings positive. The currentfrom point 15 through capacitor 44 and differential relay coil 38 backto secondary winding 24 is again the sum of the divided currents.

In a like manner, referring to FIG. 3, there is shown an equivalentcircuit loop driven by secondary winding 23 of output transformer 55, inwhich resistance 58 represents the cable resistance of remote cable 16,55 again represents the total ground resistance and inductor 13 is theprimary winding of the neutralizing transformer.

The current produced by the voltage changes in secondary winding 23flows through capacitor 44 and divides at point 12 into two parallelpaths between points 15 and 53, one path through the cable resistance 58and the second path through the primary transformer winding 13 andresistance 55 in series with it. The current again divides in a mannerinversely proportional to the impedance of each path at the outputfrequency of oscillator 19. The arrows represent the current are thesame and are in the same direction or are in phase, the current flowdepicted in FIGS. 2 and 3 is also in phase.

It will be observed, however, by close comparison between FIGS. 2 and 3,that the direction of current flow in the primary winding 13 of theneutralizing transformer due to secondary winding 24 is towards point15, while that due to the secondary winding 23 is away from point 15,and since the currents in secondary windings 23-and 24 are, as statedpreviously, always in phase with each other, these two currents buck andtend to cancel out, thus inducing no effect into the neutralizingtransformer itself. By adjusting potentiometer 36, the bucking currentin primary winding 13 due to secondary winding 23 can be adjusted toprecisely cancel the current in the primary winding 13 due to secondarywinding 24.

Since the impedance of primary winding 13 in FIG. 2 is low and theimpedance of the cable 16 shown as resistor 58 in FIG. 3 is also low,the currents through differential relay coils 38 and 30 can easily beadjusted to be approximately equal; therefore, the relay is notactivated. This then represents the balanced condition in the primaryground circuit intact. Should the primary ground circuit however open,the equivalent circuits change as shown in FIGS. '4 and 5.

Referring now to FIG. 4, the same circuit is shown as in FIG. 2, butwith cable 16 open; therefore, resistance 58 has been removed. Since thecable resistance 58 is in series with the ground resistance 55, and theground resistance 55 is high compared to the primary winding impedanceof winding 13, the current in the loop and therefore in differentialrelay coil 38 does not appreciably change. The purpose of this will beevident.

Referring now to FIG. 5, there is shown the same equivalent circuit asin FIG. 3, but again with the cable 16 open and. therefore resistance 58removed. Since ground resistance 55 is relatively high and the primarycurrent path, i.e. the cable resistance 58removed, thereis an immediatedrop in the current in the loop, and therefore in differential relaycoil 30, causing differential relay 31 to activate. Connected to thedifferential relay contacts may be an audible alarm or a visual alarmsystem such as a warning light, not depicted in the drawings because itis so well known to the art.

It should be obvious to those skilled in the art that any appreciablechange in the ground impedance 55 will also cause imbalance in thedifferential relay and trip the alarm.

It should also be obvious that any appreciable change in impedance inany element around the circuit loop points 12, 53, 15 and 12 willunbalance the currents through the upper portion of one loop and causethe relay to trip, thus a minor fault in cable 16 or a poorer corrodedconnection would cause the, alarm to trip warning of impending trouble.I

The circuit described here is but one species of this balanced alarmsystem and it should be clear that changes can be made without departingfrom the basic novelty and scope of this invention, for example, adifferential amplifier and its associated components may be used inplace of the differential relay.

That which is claimed is:

1. A monitor circuit for monitoring the primary winding ground circuitof a neutralizing transformer comprising a differential relay having afirst and a second winding and means operable upon an unbalance incurrent flowing through said first and second windings. A localoscillator having a first and a second output circuit, means forconnecting said first output circuit in series with said first windingand said primary winding and said second output circuit in series withsaid second winding and said primary winding so as to produce asubstantially equal and opposite current flow in said first and saidsecond windings and an unbalance in the current flow in said first andsaid second windings upon a change in the impedance of the primarywinding ground circuit of the neutralizing transformer.

2. A monitor circuit as set forth in claim 1, wherein said groundcircuit includes a local ground connected to one side of the primarywinding and a remote ground connected to the other side of the primarywinding, said remote ground being located outside the influence of thelocal ground.

3. A monitor circuit as set forth in claim 2, wherein said means forconnecting said first and said second windings includes separatecircuits including a balancing potentiometer connected in series withone of said first and second windings.

4. A remote monitor circuit for monitoring the primary winding groundcircuit of a substation neutralizing transformer comprising a localsubstation ground circuit for said primary winding and a remote groundcircuit for said primary winding, said remote ground circuit having aground established outside the influence of the substation ground, adifferential relay having a first and a second winding, first meansconnecting said first winding in series with the neutralizingtransformer primary winding, second means connecting said second windingin series with the neutralizing transformer primary winding, means forapplying-to said first and second winding a current flow to produceopposing forces, said relay including a switch adapted to be operatedfrom a first position corresponding to substantially equal and oppositeopposing forces to a second position corresponding to an unbalance ofthe opposing forces resulting from a change in the impedance of theprimary winding ground circuit of the neutralizing transformer.

5. A remote monitor circuit as set forth in claim 4, wherein saiddifferential relay is remote from said substation.

6. A remote monitor circuit as set forth in claim 4, wherein said remoteground circuit comprises a cable connected between one end of theprimary winding and a remote ground point, said local ground circuitcomprising a direct connection'to the substation ground from the otherend of the primary winding, said cable being connected in series withthe ground circuit of said primary winding by said first means and inparallel with the ground circuit of said primary winding by said secondmeans.

1. A monitor circuit for monitoring the primary winding ground circuitof a neutralizing transformer comprising a differential relay having afirst and a second winding and means operable upon an unbalance incurrent flowing through said first and second windings. A localoscillator having a first and a second output circuit, means forconnecting said first output circuit in series with said first windingand said primary winding and said second output circuit in series withsaid second winding and said primary winding so as to produce asubstantially equal and opposite current flow in said first and saidsecond windings and an unbalance in the current flow in said first andsaid second windings upon a change in the impedance of the primarywinding ground circuit of the neutralizing transformer.
 2. A monitorcircuit as set forth in claim 1, wherein said ground circuit includes alocal ground connected to one side of the primary winding and a remoteground connected to the other side of the primary winding, said remoteground being located outside the influence of the local ground.
 3. Amonitor circuit as set forth in claim 2, wherein said means forconnecting said first and said second windings includes separatecircuits including a balancing potentiometer connected in series withone of said first and second windings.
 4. A remote monitor circuit formonitoring the primary winding ground circuit of a substationneutralizing transformer comprising a local substation ground circuitfor said primary winding and a remote ground circuit for said primarywinding, said remote ground circuit having a ground established outsidethe influence of the substation ground, a differential relay having afirst and a second winding, first means connecting Said first winding inseries with the neutralizing transformer primary winding, second meansconnecting said second winding in series with the neutralizingtransformer primary winding, means for applying to said first and secondwinding a current flow to produce opposing forces, said relay includinga switch adapted to be operated from a first position corresponding tosubstantially equal and opposite opposing forces to a second positioncorresponding to an unbalance of the opposing forces resulting from achange in the impedance of the primary winding ground circuit of theneutralizing transformer.
 5. A remote monitor circuit as set forth inclaim 4, wherein said differential relay is remote from said substation.6. A remote monitor circuit as set forth in claim 4, wherein said remoteground circuit comprises a cable connected between one end of theprimary winding and a remote ground point, said local ground circuitcomprising a direct connection to the substation ground from the otherend of the primary winding, said cable being connected in series withthe ground circuit of said primary winding by said first means and inparallel with the ground circuit of said primary winding by said secondmeans.